Thermosensitive recording elements have wide application in the printing industry. For example, thermosensitive recording elements have been used in recording instruments for measurements such as facsimiles, printers, thermal devices for computers, devices for preparing architectural and engineering drawings, automatic vending machines for dispensing railroad tickets and luggage tags, and thermal label printing devices. Conventional thermosensitive recording elements generally comprise a support and a thermosensitive recording layer provided thereon. The thermosensitive recording layer primarily contains a binder, a substantially colorless electron donating dye precursor and an electron accepting compound, also known as a developer. Heat is applied to the element by means of a thermal head, a thermal pen or laser beam, and upon heating, the dye precursor instantaneously reacts with the electron accepting compound to form a recorded image.
Thermosensitive recording elements are typically prepared by finely dispersing the electron donating dye precursor and the electron accepting compound in an aqueous solution of a water soluble binder. For example, U.S. Pat. No. 4,717,593, issued to Igarashi et al. on Jan.5, 1988, describes a heat sensitive recording sheet obtained by applying aqueous dispersions of an electron donating colorless dye and an electron accepting compound to a base. At least one of the aqueous dispersion of the electron donating colorless dye and the aqueous dispersion of the electron accepting compound is prepared by dispersing by means of a horizontal sand mill to obtain an average particle size of about 0.5 to 3 .mu.m. Dispersions prepared in this manner are coated onto a support such as paper and the coated paper is then dried. The imaging surface of thermosensitive recording elements prepared in this manner is not very smooth. This surface irregularity causes less than optimum contact of the element with the print head of thermal recorders. Thus, non-uniform images are formed. It has been found that passing the finished thermosensitive recording element through a calender produces a smooth coated surface which provides optimum contact with the print head of thermal recorders. However, post coating calendering is disadvantageous in that (1) it requires expensive equipment and (2) it may decrease yields of the finished element and thus cause an increase in manufacturing costs.
Accordingly, a need exists for a thermosensitive recording element having improved smoothness without the disadvantages associated with conventional post coating calendering. It has been found that the thermosensitive elements of the invention overcomes these disadvantages.